Electric fire alarm system



Feb. 21, 1956 T. w. BLAND ET AL ELECTRIC FIRE ALARM SYSTEM 2Sheets-Sheet l Filed Feb. 6, 1955 INI/EN TORS B4 Awa, 4. 0 use/5M THOMASz. 41s Tse Wam/@Wwe @man Feb. 21, 1956 T. w. BLAND ET AL 2,736,012

ELECTRIC FIRE ALARM SYSTEM Filed Feb. 6, 1953 2 Sheets-Sheet 2 I N V ENTORJ` THOMAS w. 31m/v0. 535; 715e 4. o 'ae/544 United States Patent O2,736,012 ELECTRIC FRE ALARM SYSTEM Thomas W. Bland and Lester A.OBrien, San Jose, Calif., assgnors to Fire Spotter Electric Alarm Co.,San jose, Calif., a firm Application February 6, 1953, Serial No.335,446 4 Claims. (Cl. 34a- 227) This invention relates to electric lirealarm systems, and more particularly to a re alarm system havingsupervisory testing means whereby any defect in the system can bedetected, and which is adapted to respond to conditions, such asearthquakes or detonatlons, other than re.

It is among the objects of the present invention to provide an improvedelectric tire alarm system which can be easily installed in a structure,such as a building or ship, and arranged to indicate the presence oftire in any part of the building by a suitable alarm signal; whichutilizes alternating current, such as the commercial electric currentsupplied to buildings by public utility companies, and an auxiliarysource of power, such as a storage battery, and means for automaticallyswitching the system to the auxiliary power source in the event offailure of the normal power supply, and returning the system to thenormal power supply when the normal supply is restored; which includesmeans for testing the circuits or the system for detects without settingoil the alarm; which includes means for indicating the operatingcondition in which the system is disconnected from the normal powersource and connected to the auxiliary power source; which may includealarm means responsive to conditions other than tire and may providedistinctive alarms for different conditions; and which is simple anddurable in construction, economical to install, reliable in operation,and easy to test and service.

Other objects and advantages will become apparent from a considerationof the following description and the appended claims in conjunction withthe accompanying drawings, wherein:

Figure 1 is a wiring diagram of an alarm system illustrative of theinvention;

Figure 2 is a longitudinal, medial cross sectional View of a temperatureresponsive element constituting an operative component of the system;

Figure 3 is a transverse cross sectional View on the line 3 3 `of Figure2;

Figure 4 is a top plan View of a shock responsive unit constituting anoperative component of the system; and

Figure 5 is a cross sectional view on the line S-5 of Figure 4.

With continued reference to the drawings and particularly to Figure 1,the numeral l@ generally indicates a stepdown transformer foralternating current having a primary winding 1l connected at itsopposite ends to power wires 12 and 13 of a house wiring system orsimilar alternating current supply, and the numeral 14 indicates thesecondary winding of the transformer 1t). The numeral 15 generallyindicates a multiple terminal board, the numeral 16 generally indicatesan auxiliary power source, such as a storage battery, the numeral 17generally indicates the protective circuit for the lire warning meansand the numeral 18 generally indicates the tire alarm signal devicewhich is put into operation when the protective circuit is broken.

The protective circuit includes a plurality of heat responsive elements,as generally indicated at 20 and 21 in Figure l and illustrated indetail in Figures 2 and 3, connected in series with each other by aconductor wire 22.

A high resistance, electrically conductive element 32 is disposed withincuit is maintained through the protective circuit regardless of theopening of the temperature controlled switches as long as the conductorwire 22 remains intact.

Designated at 3S is a relay which controls the substitution of a battery16 for the transformer power supply responsive to the failure of saidtransformer power supply.

Designated at 65 is a relay which operates in response to the opening ofthe thermostatic switches in the detector units Ztl, 21 to energize asignal relay 68, which in turn controls a signal drop relay 105.

Designated at 125 is a supervisory relay which operates in response to abreak in the detector circuit 17 to energize a trouble signal 153.

Designated at is a relay which to the opening of the thermostatic tectorcircuit to energize signal relay 68 and signal drop relay tlS when thebattery 16 has been substituted for the transformer power supply by arelay 38.

The relay 38 comprises a winding 39 and three poles 4l?, 41 and 42. Whenthe winding is energized the pole 4l) 1s held in conductive engagementwith relay switch contacts 43 and 44, the pole 41 with contacts 45 and45 and the pole 42 with contacts 47 and 48. When the winding 3i? isde-energized the poles 4i), 41 and 42 are simultaneously moved bysuitable resilient means to move the pole 4Q away from the contacts 43and 44 and into electrically conductive engagement with contacts 50 and5l, to move the pole 41 away from contacts 45 and 46 and into engagementwith contacts 52 and 53 and to move the pole 42 away from contacts 47and 48 and into engagement with contacts 54 and 55,

A conductor 56 leads from one end of the secondary winding 14 of thetransformer 10 through Wire 91 to the operates in response switches inthe deend of the housing series connected temperature' contact 47, saidconductor 56 also being connected to one side of the winding 35. Aconductor 5.8 leads from the other end of the transformer winding 14 anda conductor 59 connects the conductor 58 to the other side of thewinding 39 so that this winding is energized as longV as the transformer10 is in operation.

One end of the conductor wire 22 ofthe protective circuit 17 isconnected to terminal 60 of the terminal board 1,5Y and this terminal 60is connected by a conductor 61 to the conductor S extending from one endof thetransformer secondary winding 14. The other end of the wire 22isconnected to terminal 62 and a conductor 63 leads from terminal 62 toone side of thewinding 64 ofthe electromagnetic drop relay 65. Aconductor 66 leads from the other side of thewinding 64 to one terminal67 of the single pole double-throw electromagnetic rela ,generallyindicated at 68having a winding 70 and a pole 7i vin electricallyconductive engagement with the Contact 67 and a secondA contact 72 whilethe winding 70 is deenergized, as it is normally when the winding 64 ofrelay 65 is energized. A conductor 73` leads from the contact 72 to acontact 74 of the electromagnetic relay switch, generally indicated at7,5, having a winding 76 and a sfingle pole 77 closed simultaneouslywithk the contact 74 and a contact 78 when the winding 76 isde-energized as it normally is. The winding 76 is deenergized as longVas winding 39 is energized by operation of the transformer 10.

VA conductor 80 leads from the contact 7Std a conductor 90 which leadsto the contact 48 of the relay 38. Eole 42 of relay 38 connects contact48 to contact 47 of this relay vand contact 47 is connected by aconductor 91 to conductor 56 leading tothe end of secondary winding 14`opposite the end of this winding from which conductor 58v extends.

This completes an energizing circuit for drop relay 65 asV long astransformer is in operation and protective circuit 17 remains closed.

One side of the main signal device 18 is connected by a conductor 94 tothe terminal 95 and this terminal is connected by a conductor 96 andconductor 61 to the conductor 5S so that one side of the signal deviceis directly connected to `the secondary transformer coil 14. The otherside of the main signal device is connected by a conductor 97 to theterminal 98 and the terminal 98 is connected by a conductor 99 to onecontact 100 of a single pole double-throw manual switch 101. The pole ofswitch 101 is connected by a conductor 102 to one contact 103 of theelectromagnetic drop relay, generally indicated at 105, and, when thepole of switch 101 is in position' for operation of the signal 1S, theterminal 98 is connected to relay drop contact 103.

The drop relay 105 is a two pole single-throw relay having avwinding 106and poles 107 and 108. The winding 106r is connected at one side to theconductor 58 by a conductor 109 and is connected at itsother side bycondoctors 110 and 111 to .a contact 11,2 of the electromagnetic relay68 and a contact 113 of the electromagnetic relay 75. lThe pole 108 ofrelay 105 connects contact 10,3 of this relay to a contact 114 of thesame relay when the winding 106 is energized and contact 114 isconnected by conductors 115 and 116 to conductor 90 leading throughrelay switch 38 to the other end of transformer winding 14 thuscompleting an energizing circuit forv signal device 18 when winding106is energized and the pole of switch 101 engages contact 100.

Winding 106 cannot, however, be energized as long as protective circuit17 is closed as the protectivecircuit maintains winding 64 energized, asexplained above, and this winding, when energized, maintains pole 118 ofrelay 65 out of contact with contacts 119 and 12o of the same relayAthus maintaining winding 70 Cre-energized and pole 71 out of engagementwith contact 112. The winding 76 of relay 75 is maintained dei-energizedwhile the system is operating on transformer current maintaining thepole 77 out of engagement with the contact 113.

It will be noted that one side of the winding 70 of the relay 68 isconnected by a conductor 121 to line 58 and that a conductor 122 leadsfrom the other side of winding 70 to a contact 123 of theelectromagnetic supervisory relay, generally indicated at 125, thewinding 126 of which is normally energized, as will be later explained,so that one pole 127 of this relay connects the contact 123 to thecomplementary contact 128. A conductor 129 leads rom contact 128 ofrelay 125 to contact 43 of relay 38 and contact 43 is connected by pole40 to contact 44 of relay 38, contact 44 being connected by conductor130 to contact of relay 65. Contact 120 is connected by pole 118 tocontact 119 of relay 65 only when winding 64 is de-energized by openingof the protective circuit 17 and contact 119 is connected by a conductor131 to line 98 leading through pole 42 to transformer lead 56.

With this arrangement, if the protective circuit 17 is opened by openingof one or more of the temperatureresponsive switches therein, thecurrent inthe energizing circuit for winding 64 will be reduced and pole118 will close the contacts 119 and 120 of relay 65. This will establishan energizing circuit for winding 70 of relay 68 moving the pole 71 othis relay into engagementtwith contacts 112 and 132, and as the contact132 is connected by conductors 115 and 116 to line 90, this will connectconductor 110 to line 90 and establish an energizing circuit for thewinding 106 of relay drop 105. When winding 106 is energized it movespole 108 into engagement with contacts 103 and 114 of relay 105 thuscompleting an energizing circuit for the main signal device 18.

When winding 106 is energized it also moves pole 107 of relay 105 intoengagement with contacts 134 and 135 to establish the followingenergizing circuit for an auxiliary signal device, generally indicatedat 136.

Contact-134 is connected through conductor 116 to line 90 and contact135 is connected through conductor 137 to the pole of single poledouble-throw, manually operated switch 138. Switch 138 has a contact 139connected by a conductor 140 to terminal 141 and this terminal isconnected by a conductor 142 with one side ofthe auxiliary signal device136. The other side of the auxiliary signal device is connected by aconductor 143 with terminal 144 and this terminal is connected byconductors 96 and 61 to line 58.

A buzzer, generally indicated at 145, is connected at one side to line58 by a conductor 146 and at its other side by conductor 147 toalternate Contact 148 of switch 101 and alternate contact 149 of switch138. When the pole ofk switch 181 is connected to contact 148 instead ofcontact 100 and pole 108 of relay drop 105'closes with contactsy 114 and103 the buzzer 145 will be energized instead ofthe signal device 18 andsimilarly, lwhen the pole of switch 138 is closed with contact 149instead of contact 139 andV pole 107 of relay 105 closes with contacts134 and 135 the buzzer 145 will be energized instead of the auxiliarysignal device 136.

The buzzer will be used principally while the sys-` tem is beinginstalled, repaired or tested so that the operative condition of thesystem can be indicated without giving a false tire alarm.

It is contemplated that the main signal device 18 will be located in thebuilding in which the system is installed and may be provided inmultiple if desired, while the auxiliary signal device 1,36 will bedisposed in some other location, such as a superintendents ofi-ice or anearby iire station. The buzzer 145 will ordinarily be mounted in thecabinet in which the various terminals, relays and switches are housed.

When the winding 64 of relay 65 has been de-energzed by interruption ofthe protective circuit 17 it will Vnot be re-energized when theprotective circuit 17 is restored because the winding 70 of relay 68 isnow energized interrupting the energizing circuitl for'winding 6'4 atcontact 67 A circuit energizing circuit from of relay 68. In order tore-energize winding 64 reset switch 150, which is a normally open, pushbutton switch, is manually closed. This establishes an energizingcircuit for winding 64 from line 58 through conductor 61, terminal 60,protective circuit 17, terminal 62, conductor 63, winding 64, conductor151, reset switch 150, conductor 152, line 90, contacts 47 and 48 andpole 42, and conductor 57 to transformer lead 56. As soon as winding 64is reenergized it opens the energizing circuit for winding 70 at contact120 and this restores the system to its normal operating condition.

The system is constantly supervised by a circuit including thesupervisory relay 125 and the trouble alarm signal 153. The winding 126of relay 125 is constantly energized by a circuit from line ortransformer lead 58 through conductor 61, terminal 60, protectivecircuit 17, terminal 62, conductors 63 and 154, resistance 155,conductor 156, pole 41 of relay 38, conductor 157, adjustable rheostat158, conductor 159, winding 126 and conductors 160 and 152 to line 90.While winding 126 is energized,

pole 127 is held out of engagement with contacts 161 and 162.

If winding 64 is de-energized by opening of one or moretemperature-responsive switches in the protective circuit 17, causingpole 163 of relay 65 to bridge contacts 164 and 165, short circuitingresistance 155, the shunting resistance 155 is compensated for by theinsertion of resistance elements 32 in the protective circuit, asbalanced against the resistance 155 by the proper adjustment of rheostat158 so that winding 126 is energized by current regardless of Whetherwinding 64 is energized or de-energized.

When winding 126 is de-energized by a complete break in the protectivecircuit, pole 127 of relay 125 moves into engagement with contacts 161and 162 establishing a circuit from contact 161 through conductor 166,terminal 167, conductor 168, trouble signal battery 169, conductor 170,terminals 167', conductor 172, trouble signal device 153, conductor 173,terminal 174 and conductor 175 to terminal 162.

When pole 127 of relay 125 moves into engagement with contacts 161 and162 to complete the trouble alarm circuit, it moves away from contacts128 and 123 breaking the energizing circuit to winding 70 of relay 68 sothat this winding cannot be energized to establish the circuit forenergizing signal device 18 thus precluding the giving of a false alarmby an accidental break in the protective circuit. The trouble signalwill remain in operation until the protective circuit is repaired or theenergy of battery 169 depleted.

Current supplied to winding 126 through resistance 155 or resistances 32and rheostat 158 is suflicient to energize relay 125 but not suicient toenergize relay 65.

In the event of power failure to the transformer 10,

winding 39 of relay 38 is tie-energized and this automaticallydisconnects the system from the transformer and connects it totheauXiliary power source 16. De-energization of solenoid 39 frees thespring means of relay 38 to move pole of this relay away from contacts43 and 44 and into engagement with contacts and 51, pole 41 away fromcontacts 45 and 46 into engagement with contacts 52 and 53 and pole 42away from contacts 47 and 48 and into engagement with contacts 54 and55. Movement of pole 42 away from contact 47 completely disconnects thetransformer winding 1.4 from the system and precludes anyre-energization of winding 39 until power is restored to thetransformer.

With winding 39 of relay 38 tie-energized, a protective the auxiliarypower source 16 is established as follows:

Beginning with terminal at one end of the protective circuit, conductorwire 22, through conductor 61 to line 58, through a portion of line 58,which is now otherwise de-energized, to conductor 176 throughinterconnected substantially the same 6 terminals 177 to conductor 179to one side of battery 16. From the other side of the battery throughconductor 180 to terminal 181, thence through conductor 182 includingfuse 183, contact 54 of relay 38 and through pole 42 of this relay tocontact 55. From contact 55 through a portion of conductor 90 andconductor 80 to contact 78 of relay 75. From contact 78 through pole 77,contact 74, conductor 73, contacts 72 and 67 and pole 71 of relay 68 andconductor 185 to conductor 66 and one side of wind ing 64 of relay 65.From the other side of winding 64 through conductor 63 to terminal 62and the other end of conductor wire 22 thus maintaining the relayWinding 64 energized as long as the protective circuit 17 remainsclosed.

The relay 65 is slow acting so that it will not move its pole 118 intoengagement with contacts 119 and 120 while the relay 38 is changing fromthe normal power connection to the auxiliary power connection.

if the winding 64 now becomes de-energized by opening of one or more ofthe temperature-responsive elements in the protective circuit 17, thepole 118 of this relay closes with the contacts 119 and 120. A circuitis now established from one side of battery 16 through conductor 180,terminal 181, conductor 182, pole 42 of relay 38, conductor 98 toconductor 131, conductor 131 to pole 118 of relay 65, conductor 130,pole 40 of relay 38, conductor 187, contacts 188 and 189 and pole 190 ofrelay 125, conductor 191, winding 76 of relay 75, conductor 192,conductor 58, conductor 176, terminals 177, and conductor 179 to theother side of battery 16 thereby energizing winding 76 of relay 75 andclosing pole 77 of this relay with contacts 193 and 113 of this rela f.

When Winding 76 is energized, a circuit is established from battery 16through conductor 180, terminal 181, C011- ductor 182, contacts 54 and55 and pole 42 of relay 38, conductor 98, conductor 80, contacts 193 and113 and pole 77 of relay 75, conductor 110, winding 186 of signal drop105, conductor 109, a portion of conductor 58, conductor 176, terminals177 and conductor 179 to the other side of battery 16 thereby energizingthe signal drop relay 105.

When the signal drop relay is energized a main signal energizing circuitis established from battery 16 through conductor 180, terminal 181,conductor 182, contacts 54 and 55 and pole 42, conductor 90, conductor116, contacts 114 and 103 and pole 108 of signal drop 105, conductor102, switch 101, conductor 99, terminal 98, conductor 97, main signaldevice 18, conductor 94, terminal 95, conductors 96 and 61, conductors58 and 176, terminals 177 and conductor 179 back to the other side ofbattery 16.

At the same time the auxiliary signal circuit is established fromconductor 116 through contacts 134 and 135 and pole 107 of signal drop105, conductor 137, switch 138, conductor 140, terminal 141, conductor142, auxiliary signal device 136, conductor 143, terminal 144 andconductors 96 and 61 to line 58.

After the winding 64 has been de-energized, it is reenergized by closingthe reset switch 150 establishing a re-energizing circuit from the line58 through the protective circuit and winding 64 to the line 90 asdescribed above.

The supervisory circuit maintaining the winding 126 of relay 125energized is also the same as that described above except that conductor157 is now dead and is substituted by conductor 195 leading from contact52 of relay 38 through adjustable rheostat 196 and conductors 197 and159 to winding 126.

The shock alarm apparatus comprises a normally held open microswitch 208having a terminal 201 connected by conductor 202, terminal 203 andconductor 204 to line 58 and a pole 205 connected by conductor 286 toone side of a signal device 287. The other side of signal device 207 isconnected by a conductor 208. terminal 209, and

conductor 239 to line 9@ and with this arrangement signal device 267will be energized when microswitch G closes regardless of whether thesystem is operating on normal or auxiliary power.

As shown in Figures 4 and 5, the microswitch 200 is pivotally mounted atone end by a hinge connection 22 on a horizontally disposed base T13 andhas `its operating plunger 214 projecting from its side remote from thebase and adjacent the free end thereof. Three internally screw threadedsleeves 2id, 2id and 217 extend through the base and are located at theapices of an equilateral triangle. Screws M8, 2id and 226 are threadedthrough the sleeves 215, 2l6 and 27 respectively and the center lines ofthese screws converge upwardly to a common point disposed above the base2id. The switch plunger 2id has its center line substantially coincidentwith a line extending through the point ot' convergence of the centerlines of the screws 2id, 2ll9 and 229. A sphere 22l of heavy material,such as metal rests on the upper ends of the screws which provide atripod support for the sphere or ball, and the ball presses downwardlyon switch plunger 2id maintaining switch 26S open until the ball isdislodged from its support on the upper ends of the screws by a shock,such as an earthquake tremor.

The screws can he moved upwardly or downwardly relative to the base 213to adjust the sensitivity of the device, the device becoming moresensitive as the screws are moved upwardly bringing their Lipper endscloser together.

A fourth screw threaded sleeve 222 extends through the base 213 at thecenter of the triangle formed by the sleeves 215, 2id and 217 and ascrew 223 threaded through sleeve 222 bears at its upper end against theunderside of the housing of microswitch Zilli to maintain the properpressure of sphere on switch button or plunger 21d as the -screws 213,2l9 and 22@ are moved relative to the base 2l3 to raise or lower thesphere Timing relays, as generally indicated at 224 and 225 a -econnected between the switch 2%@ and the earthquake alarm signal deviceZit-i7. rhe relay 224% is a slow-acting relay and has a winding 27.5connected between conductors 2% and 2% by conductors 227 and 22d. Arelay oV-and-on control switc. 229 is connected into the conductor 227and a relay-operated switch 234) is connected into the conductor 2% toprovide intermittent operation of the signal 207.

The timing relay 225 is a fast-operating relay and includes a winding231 connected between conductors 206 and 29%,? by conductors 232 and233, an. oi-and-on control switch 234.1 in the conductor 252 and arelay-operated switch 235 in the conductor 206 to provide anintermittent operation of the signal device 2&7.

The relays 224 and 22S are to be used alternatively and a manuallyoperated switch 236 is connected in shunt of the microswitch Zitti sothat the earthquake alarm device can be manually operated if desired.

The invention may be embodied in other specic forms without departingfrom the spirit or essential characteristics thereof. The presentembodiment is, therefore, to be considered in all respects asillustrative and not restrictive, the scope of the invention beingindicated by the appended claims rather than by the foregoingdescription, and all 'changes which come within the meaning and rangeot` equivalency of the claims are intended to be embraced therein.

What is claimed is:

l. An electric re alarm system comprising a protective circuit includingnormally closed temperature-responsive switches connected together inseries, a resistance element connected across eachtemperature-responsive switch in shunt thereof, a source of electricalenergy, a re alarm signaly device, a circuit trouble signal device, acontrol relay connected in series with said energy source and saidprotective circuit and having switch means and a winding normallyenergized as long as all of said temperatureresponsive switches areclosed, said temperature-respon;

winding connected in series with said energy source and the switch meansof said control relay and energized when the winding of said controlrelay is de-energized, said signal drop relay having switch meansconnected in series with said energy source and said lire alarm signaldevice eiective to establish an energizing circuit for said re alarmsignal device when the coil of said signal drop relay is energized, asupervisory relay having a winding conected in series with said energysource and said protective circuit means arranged to energize saidsupervisory relay only as long as said protective circuit is continuousthrough the resistance elements connected across saidtemperature-responsive switches, and switch means formed and arranged toestablish an energizing circuit for said circuit trouble signal devicewhen the winding of said supervisory relay is deenergized.

2. An electric alarm signal system comprising a source of electricalenergy, a signal device, a protective circuit, a rst electromagneticrelay having a winding and a switch, an energizing circuit for thewinding or" saidrst relay including said source of electrical energy,said protective circuit and the winding of said rst relay and formed andarranged to place the switch of said irst rclay in one condition 'whensaid protective circuit is closed and in a second condition when saidprotective circuit is open, a second circuit including said source ofelectrical energy, the switch of said first relay and said signal deviceformed and arranged to energize said signal device when the switch ofsaid iirst relay is in said second condition, a circuit of highelectrical resistance extending along said normally closed protectivecircuit and connected and parallel therewith, means to maintain saidhigh resistance circuit closed when said protective circuit is opened, asecond electromagnetic relay having a winding and a switch connectedinto said Second circuit, a third circuit including said source ofelectrical energy, said circuit of high electrical resistance and thewinding of said second relay, a trouble alarm device, a source ofelectrical energy for said trouble alarm device, and a fourth circuitincluding the switch of said second relay, said trouble alarm device andthe source of electrical energy for said trouble device, means tomaintain said fourth circuit closed to energize said trouble alarmdevice and to open said second circuit to preclude giving a false alarmwhen said third circuit is opened by breakage of said circuit of highelectrical resistance.

3. An electric re alarm system comprising a protective circuit includingnormally closed temperatureresponsive switches connected together inseries, and resistance elements connected across eachtemperature-responsive switch in shunt therewith, a source of electricalenergy, a tire alarm signal device, a circuit trouble signal device, acontrol relay connected in series with said energy source and saidprotective circuit and having switch means and a winding normallyenergized as long as all of said temperature-responsive switches areclosed, said temperature-responsive switches being arranged to open uponabnormal rise in temperature, whereby the resistance elements aresubstituted for the temperatureresponsive switches, said resistanceelements being sumciently large in value to reduce the current in saidpro tective circuit sutlciently to de-energize said control relay, meansto energize said re alarm device when the winding of said control relayis deenergizeda supervisory relay having a winding connected in serieswith said energy source and said protective circuit, means arranged toenergize said supervisory relay only as long as said protective circuitis continuous through the resistance elements connected across saidtemperaturereis tie-energized.

4. In an electric tire alarm system, a protective circuit including anormally closed temperature-responsive switch arranged to openresponsive to a predetermined rise in temperature, a resistance elementconnected across said switch in shunt therewith, a source of electricalenergy, a fire alarm signal device, a circuit trouble signal device, acontrol relay connected in series with said energy source and saidprotective circuit and having a winding normally energized as long assaid temperatureresponsive switch is closed, means to energize said firealarm device when the winding of said control relay is deenergi2ed, asupervisory relay having a winding connected in series with said energysource and said protective circuit, means arranged to energize saidsuper visory relay only as long as said protective circuit is continuousthrough the resistance element connected across saidtemperature-responsive switch, said temperature-responsive switch beingarranged to open upon abnormal rise in temperature, whereby theresistance element is substituted for the temperature-responsive switch,said resistance element being suciently large in value to reduce thecurrent in said protective circuit suiciently to de-energize saidcontrol relay, and means formed and arranged to establish an energizingcircuit for said circuit trouble signal device when the winding of saidsupervisory relay is de-energized.

References Cited inthe le of this patent UNITED STATES PATENTS

